Treaty And Custom As Sources of International Law

By Trokon N. Roberts, Sr,

Student ID NO:  GP93327

Cuttington University Graduate School Of Global Affairs Ans Policy

Tubman Boulevard – Monrovia, Liberia


It was no mistake when world leaders got together and put into place, for the sake of peace, security, international coordinated relations, guidelines and rules to govern the behavior of the nations of the world. There are four sources of international laws as per our study. The four sources are: Convention/Treaty, Customs, General Principles of Law, Teachings and highly qualified publicists. For the benefit of this essay, discussions will focus on the two major sources of international laws, which include Treaty/Convention and Customary Laws. The essay is intended to provide analyses of treaties and customary laws from an international law standpoint. At the end of the essay, you will know what treaties and customary laws are. You will also know the difference between the two and how they can be applied to serve the best interest of society as far as international laws and relations are concerned. For the essence of this essay, conventions/treaties will be analyzed in the subsequent paragraph.


Interchangeably, conventions and treaties are generally the same. They are written agreements between two or more states that are governed and under the auspices of international laws. They can also be referred to as agreements, conventions, protocols, and exchanges of notes. In order to have a binding effect on treaties, there is a law that governs them which is referred to as the ‘the Law of Treaty’. This law of treaty can now be found in the 1969 Vienna Convention on the Law of Treaty. It contains guidelines, procedures, basic principles of how treaty can be binding and entered into force. Also included in these laws are principles of how these laws can be interpreted and disciplinary measures that are meted out against states that breach the laws. Treaties can be bilateral, multilateral, regional, or global ( Examples: Mano River Union (MRU) is a multilateral treaty because it includes Guinea, Sierra Leone, Ivory Coast, and Liberia while the European Union contains twenty-seven (27) European states with binding objectives and goals.

The Binding Force of Treaties: 

It has to be born in mind that treaties are not local laws that come into force with binding authority without consent of the objects. Nevertheless, they are only binding on States who are signatories to the particular treaty, and hold no binding effect or obligations to a third state without the consent of that state. In order for a treaty to be authentic and binding, it must be based on actual consent and assent, and must be expressed by signature, ratification and accession (SRA). If a state is a signatory to an international treaty or convention, it must send an ‘instrument of ratification’. That is, that state must indicate its willingness and intention to be a part of a particular treaty. Ratification is an approval process by states that supersede the signature of the treaty. On the other hand, if the state is not a signatory to the treaty or international convention (as it may also be called), but decides to be a party to the treaty, that state should send an instrument of accession. Accession is a process by which a state is not a part of a treaty. Like ratification, it also has similar legal implications. A significant point to note is that a state can be a signatory to a treaty but it is not bound by the treaty but is under moral obligations to not to be involved with any acts that will defeat the goals, objective, and aims of said treaty (Beckman, R. & Butte, D. (nd)).

In order to be bound by a treaty, a state must express its consent by the provisions of the treaty by depositing an instrument of accession or ratification to the main or official depository of said treaty. However, the legal implications on the two documents remains the same. As long as a state expresses its consent and desires and complies with the standards set to be bound and the treaty is in force, it is then referred to as a party to the treaty. A third party has no obligations, bound, or rights to a treaty because it made no consent. Generally, by principles, only signatories to a treaty are under binding obligations to adhere and comply with the terms. In general, the rule is that ‘a treaty shall be interpreted in good judgment to cope with the ordinary meaning that reflects the actual definition and meaning of the treaty in terms of its purpose, and objective (1969 Vienna Convention).

Customary Laws:

It can be recalled many significant areas of general international laws are based on Customary Laws. Customary Law is the oldest, original and the main source of international law. The customary norms of international laws come about when States act in a particular way because they believe they are under obligation to do so by law (the so-called opinio juris sive necessitates, in short opinion juris). By one definition, customary law is law of customs that are accepted as legal requirements or obligatory rules of conduct; practices and beliefs that are so vital and intrinsic a part of a social and economic system that they treated as if they were laws (ICRC). Some examples of customary laws are: laws against piracy, laws against slavery, laws against terrorism, etc.,  ( This in itself requires a general widespread and consistent of State practice. States who allege the existence of a rule of customary law has the responsibility by showing a coordinated practice among member states. This involves states mainly affected by the rule or having biggest interest in the matter. Let’s take for example, in order to examine the behavior of member states on military issues like outer space operations, a crucial look has to be taken of member states carrying out activities in space. In other words, member states who are involved with alleged customary laws do so, being knowledgeable of the legal implications (opinion juris) rather than out of comity or for political reasons.

Illustrations and Practicum of Customary International law

Some key examples of customary international customary laws are Non-Refoulement, and Granting Immunity to a visiting President. The non-refoulement principle of international law forbids a country, having received refugees as asylum seekers from returning them to their country of origin where they could likely face prosecution based on their race, religion, nationality, membership of a particular social group or political party (UNHCR, 1951 Refugee Convention). Some examples of refoulement are: Llias and Ahmed Vs Hungary /application no. 47287/15. Another incident is that of the alleged action of Tanzania’s in 1994 to have sent back Rwandese back home. UNHCR then vowed that they should be repatriated voluntarily. The granting of immunity to visiting heads of state is another pertinent example as far as custom laws are concerned. A good example of this is the refusal of South African government under the leadership of Thabo Mbeki to hand over Omar Al-Bashir in 2015 to the International Criminal Court which the Sudanese leader was visiting Johannesburg in South Africa (W. Nortje, 2017). Due to this decision the South African government attempted to pull out of the ICC. However, the government of South Africa sees itself as an important element in a new global system that seeks international justice, peace, security and a new global governance initiative.

Elements of Customary International Law: 

There are two elements of international customary laws. The two elements are State Practice and Opino Juris sive neccessitatis. The widespread reputation by states of similar international acts over a period of time can be considered the State Practice while the requirements that the acts must occur out of a sense of obligations (Opinio Juris) (Beckman, R. and Butte, D. (n.d)). Customary laws change from time to time. The flexibility and ability to change remains a significant feature of customary laws. It is incumbent upon traditional authorities to rightfully make new customary laws and make the necessary amendments and repeal existing customs when the need arises. However, these laws should be in the context of the very community. A significant advantage of customary law is that it is not necessary for a state to formally accept a rule in order to be bound by it, as long as the overall State on which the rule is based is “spread widely, representative and virtually uniformed” and accepted as law (

In conclusion, treaties bind only those States which have expressed their consent to bound them, this is done usually through ratification; whereas, customary international law, on the other hand derives from “a general practice accepted as law (

Note: This essay was submitted to Dr. Mory Sumaworo (Ph.D.), a lecturer at Cuttington University Graduate School of Global Affairs and Policy as a part of the Components of the International Law Course.


Beckman, R. & Butte, D (n..), “Introduction to International Law”
Customary Law, Traditional Knowledge

( overview_customary_law

(ICRC) Customary Law


N. Windell, (2017) FICHL Policy Brief Series – No 85
UNHCR, 1951 Refugee Convention


United Nations, Vienna Conventions on the Law of Treaties (1969)


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